Reproducible incisions are required for a variety of medical procedures. For example, blood samples are drawn routinely from patients (including neonares) for use in numerous types of blood tests such as mandatory screening tests for conditions like phenylketonuria (PKU) and low thyroid function and for measurement of bilirubin levels to monitor jaundice. The blood needed for many tests is conventionally drawn by creating a small incision in the patient's skin. Typically, such incisions are made on the patient's fingertip. For infants or patients with poor circulation, however, the incision can be made in alternate areas such as the foot, arm, or leg.
It is often necessary, as for example when surgery is contemplated or when the patient is a newborn infant, to determine if the patient suffers from a disorder or the effects of medication which may abnormally affect the patient's bleeding time (the time during which blood flows from an incision before coagulation stops the flow). Therefore, in order to test the bleeding time, it is necessary to form a reproducible incision on the patient and to measure the time required for bleeding to stop. The test may be repeated later to check for improvement or deterioration in the bleeding time and, in that case, it is imperative that the incision formed be of approximately the same length and depth as the previous test incision.
The device normally used to create the needed incision in the patient for many medical procedures is a mechanical lancet device. In the development of the art for mechanical lancet devices, many different designs have been created. The most modern of the designs typically are disposable; reusable devices present sterility problems and create a hazard of contamination to both patients and attendants. Such designs also have automatically retractable blades and other operations that prevent their reuse after a single incision has been made and reduce the risk of injury and contamination.
A common feature of the lancet devices is that they make incisions using a plunge cut: the cutting blade is plunged through the skin traveling perpendicular to the skin. One disadvantage of a plunge cut is that the size of the incision matches the size of the cutting blade. Typically, the pointed blade creates a V-shaped incision. The widest region of the incision is on the surface of the skin; the narrowest region of the incision coincides with the deepest point of the incision. Because the narrowest point of the cut is also the deepest point of the cut, a relatively deep incision must be made to ensure that enough capillaries are severed to achieve the necessary bleeding.
Another disadvantage associated with plunge cut lancet devices is that they are painful. A plunge incision is more traumatic than a slice incision. Slice incisions are less intrusive and heal more readily. Moreover, plunge cuts may cause skin tissue, skin fluids, or both to mix with the blood, thereby producing tainted blood samples. Finally, the wide range of skin toughness renders most plunge-type lancet devices unreliable in the accuracy and repeatability of the depth of the cut.
Consequently, slice action devices are often used to create incisions which facilitate blood sampling for medical tests. A blade slices across the patient's skin causing an elongated incision. Conventional slicing lancet devices use a cutting blade that is spring-loaded within a housing. The housing is placed against a patient's skin and the blade is released. The potential energy stored within the spring bias of the blade then causes the blade to exit the housing and to create the needed incision in the patient's skin.
Devices that release the energy stored in a prestressed spring during actuation and to make an incision are often unreliable in the accuracy and repeatability of the incision. Problems exist in accurately and uniformly reproducing, in practice, the tensile strengths and behavior of the spring both in compression and upon release. Such problems are exacerbated when the spring must be incorporated into a relatively inexpensive, disposable product. These difficulties are caused not only by the problems inherent in selecting and properly mounting and pretensioning the spring itself, but also by the problems in maintaining uniformity of the related components with which the spring interacts. Among other problems, dimensions must be accurately maintained and frictional forces must be controlled.
Specifically, for example, a prestressed spring (whether plastic or steel) will creep over time. Creep is accentuated if the device is stored at elevated temperatures; therefore, a shelf-life problem arises. The effect of creep is to change the physical properties of the spring: varying the flight path of the blade and the force to actuate the device, at a minimum, and, in the extreme, risking rupture of the spring.
Some slice action devices use multiple spring arrangements. Such assemblies are relatively complex and require a number of interfitting parts which are relatively difficult to manufacture and accurately assemble. Moreover, the interaction of two oppositely acting springs--typically one to actuate the blade and one to retract the blade--generates a number of design problems.
Finally, a device which incorporates a prestressed spring always risks inadvertent actuation. This is true even if the device incorporates a safety mechanism. The user may remove the safety mechanism well before use of the device is intended.
In many slicing lancet devices, cuts are created which are much longer than they are deep. Consequently, the resulting incision is limited to a body part having a relatively large surface area and is impractical for a fingertip or a neonate. Because sensitive nerve endings populate the skin surface, longer incisions often induce a significant amount of pain in the patient.
In view of the above, it is the principal object of the present invention to provide a simple, automatic device capable of producing and reproducing uniform incisions of precise location, length, and depth to facilitate blood sampling. A related object is to provide a disposable device capable of a single use only. Further objects are to provide a device which is easy to handle and which can be operated with minimal effort.
Another object is to provide a device that creates an incision using a slicing action to provide a clean, sterile cut with reduced trauma to the tissue surrounding the incision and minimal pain to the patient. Furthermore, it is an object to prevent the patient from seeing the often unsettling scene of his or her skin actually being cut and, thereby, to reduce apprehension in a patient.
A further object is to provide such a device which may be readily triggered to form the desired incision but which, before use, may be safely handled and stored without danger of the device being accidentally triggered.